This research study involves children with HIV infection and will look at the safety, tolerance and pharmacokinetics of a new protease inhibitor, Viracept, when given in different dosages orally to subjects. Children will receive Viracept orally as outpatients over 6 weeks. Viracept may be made available to subjects after the initial 6 weeks for a total of 6 months or until Viracept is licensed or withdrawn from use.